Pat pork shoulder dry; place in a slow cooker. Pour root beer over pork.

Combine brown sugar, cumin, paprika, salt, black pepper, garlic powder, onion powder, and oregano in a small bowl; sprinkle on top pork and lightly rub until entire surface coated.

Cook on Low for 5 hours; increase heat to High and continue cooking until pork is tender and easily pulled apart with a fork, about 3 hours more.

Carefully transfer pork to a platter; shred with 2 forks. Drizzle some cooking liquid over pork to moisten.